The present invention relates an ammonia refrigerating unit using a working fluid comprising an ammonia refrigerant and a lubricant containing a polyether compound having a specific structure.
A compression refrigerator generally comprises a compressor, a condenser, an expanding mechanism (an expansion valve etc.) and an evaporator and thereof, a chlorine-containing fluorohydrocarbon (flon compound) such as trichlorofluoromethane (R11), dichlorodifluoromethane (R12) or chlorodifluoromethane (R22) has been heretofore used as the refrigerant for a longtime. These flon compounds cause an international environmental problem such as ozone depletion and therefore, the use thereof is regulated and these flon compounds have been converted to a chlorine-free flon compound such as difluoromethane (R32), tetrafluoroethane (R134 or R134a) or difluoroethane (R152 or R152a). Even in these chlorine-free flon compounds, a fear of global warming is very high and therefore, an anxiety of causing environmental problem is being pointed out from the long-term standpoint.
Accordingly, in recent years, hydrocarbon, ammonia or the like has been noticed again as a refrigerant not causing such an environmental problem. From the standpoint of the adaptability and the safety to the global environment or the human body, these refrigerants are extremely excellent as compared with a flon compound. Moreover, although these compounds were not predominant as a refrigerant until now, they also have the actual result used for many years.
So far, ammonia is not compatible with a mineral oil or an alkylbenzene (which is a refrigerator oil) used in a refrigerator and therefore, the use thereof has been heretofore limited only to a refrigerator provided with an oil circulatory system where an oil separator having high performance is provided at the outlet side of a compressor, an oil is separated and recovered so that the oil is not carried out to a refrigerating cycle and again returned to the inlet side of the compressor. When such an oil circulatory system does not have a sufficient function, a refrigerator oil is carried out to the inside of a refrigerating cycle to incur shortage of the compressor lubricating oil, with the result that, a seizure or the like is brought about due to lubrication failure at a sliding portion, and the unit life may be remarkably shortened. An evaporator is a low temperature and therefore, a high-viscosity refrigerator oil carried out to the inside of a refrigerating cycle is remained in the evaporator, with the result that the heat exchange efficiency may be lowered. Accordingly, a refrigerating unit using ammonia was limited to an industrial unit which is a relatively large-size liquid pump type unit performing a forced circulation and in which a maintenance of regularly recovering an oil accumulated at a low temperature portion can be performed.
However, to overcome the above-described environmental issues, a refrigerating unit using ammonia as the refrigerant is being reconsidered. Accompanying the tendency, a working fluid which has the compatibility with an ammonia refrigerant and can be used for a refrigerating unit without an oil circulatory system similarly to the flon refrigerant, has been proposed. For example, European Patent No. 0490810 discloses a lubricant comprising a polyalkylene glycol which is a copolymer of ethylene oxide (EO) and propylene oxide (PO) and has the EO/PO ratio of 4/1. European Patent No. 585934 discloses a lubricant comprising a monofunctional or a difunctional polyalkylene glycol having the EO/PO ratio of 2/1 to 1/2. German Patent No. 4404804 discloses a polyether compound-based lubricant represented by the general formula: ROxe2x80x94(EO)xxe2x80x94(PO)yxe2x80x94H [R is C1 to C8 alkyl group, and x and y each is a number of 5 to 55]. European Patent No. 699737 discloses a lubricant represented by the general formula: Z{xe2x80x94O(CH2CH(R1)O)nxe2x80x94(CH2CH(R1)O)mxe2x80x94H}p [Z represents C6 or more aryl group or C10 or more alkyl group, R1 represents a hydrogen atom, a methyl group or an ethyl group, n represents 0 or a positive number, m represents a positive number and p represents a number corresponding to the valence of Z].
JP-A-5-9483 and International Patent Publication WO94/12594 disclose a lubricant which comprises polyalkylene glycol diether and is excellent in the compatibility with ammonia and the stability in an ammonia atmosphere.
When a polyalkylene glycol-based compound as described above is used as a lubricant component of a working fluid for a refrigerating unit using an ammonia refrigerant, it is pointed out that a polyfunctional polyalkylene glycol having two hydroxyl groups has a problem in the stability and the moisture absorption. The polyalkylene glycol diether as described above has a problem in that it is low in the compatibility with ammonia as compared with polyalkylene glycol containing a hydroxyl group and is not compatible with ammonia depending on the structure. The polyalkylene glycol diether also has a problem in that the terminal of the molecule is blocked up with an alkyl group but the production process becomes complex because of performing the terminal blockade.
Accordingly, an object of the present invention is to provide a refrigerating unit using ammonia as the refrigerant, which uses a working fluid composition comprising a mixture of an ammonia refrigerant and a lubricant having excellent compatibility with ammonia as well as superior lubricity and the stability and which does not demand an oil circulatory system.
Therefore, the present invention relates to an ammonia refrigerating unit, in which a refrigeration or heat pump cycle is formed by a refrigerating cycle, characterized by comprising a refrigeration compressor, a condenser, an expansion mechanism such as an expansion valve, and an evaporator, characterized in that a working fluid is circulated in the refrigerating cycle, the working fluid including ammonia and a lubricant that contains a polyether compound mixed in a compatible state with the ammonia and represented by one of the following general formulae (1) and (2):
X{xe2x80x94Oxe2x80x94(AO)nxe2x80x94H}pxe2x80x83xe2x80x83(1)
[wherein X represents a residue resulting from removing a hydroxyl group from a monool or a polyol, (AO)n represents a polyoxyalkylene group constituted by copolymerization of an ethylene oxide and an alkylene oxide having 3 or more carbon atoms, n represents a number of 2 or more, p represents the valence number of X, and the number of the secondary hydroxyl groups from among hydroxyl groups located at the structural terminal is 50% or more of the total number of the hydroxyl groups]
X{xe2x80x94Oxe2x80x94(AO1)axe2x80x94(AO2)bxe2x80x94H}pxe2x80x83xe2x80x83(2)
[wherein X represents a residue resulting from removing a hydroxyl group from a monool or a polyol, (AO1)a represents a polyoxyalkylene group constituted by copolymerization of an ethylene oxide and an propylene oxide and/or a butylene oxide, AO2 represents an oxyalkylene group having 3 or more carbon atoms, a represents a number of 2 or more, b represents a number of 1 or more, and p represents the valence number of X].
Further, the present invention relates to an ammonia refrigerating unit, characterized in that in the refrigerating cycle, a ratio of the ammonia refrigerant and the lubricant is 99:1 to 50:50 in terms of the weight ratio.